Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753433AbbGQX1a (ORCPT ); Fri, 17 Jul 2015 19:27:30 -0400 Received: from v094114.home.net.pl ([79.96.170.134]:60326 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751901AbbGQX12 (ORCPT ); Fri, 17 Jul 2015 19:27:28 -0400 From: "Rafael J. Wysocki" To: "Brown, Len" Cc: Austin S Hemmelgarn , Pavel Machek , Len Brown , "linux-pm@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 1/1] suspend: make sync() on suspend-to-RAM optional Date: Sat, 18 Jul 2015 01:54:09 +0200 Message-ID: <1684935.fYtBRJbzgO@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/4.1.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: <1A7043D5F58CCB44A599DFD55ED4C948468A7978@fmsmsx115.amr.corp.intel.com> References: <1436927091-32520-1-git-send-email-lenb@kernel.org> <55A668FE.80409@gmail.com> <1A7043D5F58CCB44A599DFD55ED4C948468A7978@fmsmsx115.amr.corp.intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2183 Lines: 57 On Wednesday, July 15, 2015 02:58:22 PM Brown, Len wrote: > > > -----Original Message----- > > From: Austin S Hemmelgarn [mailto:ahferroin7@gmail.com] > > Sent: Wednesday, July 15, 2015 10:07 AM > > To: Pavel Machek; Len Brown > > Cc: rjw@rjwysocki.net; linux-pm@vger.kernel.org; linux- > > kernel@vger.kernel.org; Brown, Len > > Subject: Re: [PATCH 1/1] suspend: make sync() on suspend-to-RAM optional > > > > On 2015-07-15 02:43, Pavel Machek wrote: > > > On Tue 2015-07-14 22:24:51, Len Brown wrote: > > >> From: Len Brown > > >> > > >> The Linux kernel suspend path has traditionally invoked sys_sync(). > > >> > > >> But sys_sync() can be expensive, and some systems do not want > > >> to pay the cost of sys_sync() on every suspend. > > > > > > Have you measured how expensive it can be, and why it is expensive? > > > How expensive it is can vary widely, but it pretty much boils down to > > how much dirty data still needs written out, and how slow the storage it > > needs written to is. There's not really much that can be done in the > > kernel to change this, and most userspace suspend systems call sync > > themselves during the suspend sequence. > > Right. > And now, user-space gets is no longer forced to incur that > delay on every suspend if they do not want it. > > Yes, have measured this under many conditions. > The bottom line is that sys_sync() is rarely as fast as 1ms, > and is sometimes as slow as hundreds of ms. > > >> Why do you need CONFIG parameter? > > So that an OS that doesn't want to change their user-space, > can build a kernel that does what they want by default. > > Originally I had the config parameter remove this code entirely, > which would achieve the same goal. > But Rafael prefers the sysfs attribute always exist > and the config simply set the default. Indeed. And so I'm queuing this patch up for 4.3 (with a couple of minor fixups). Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/